how to acpi shutdown in assembly in custom os?

Question

I am running a custom os in virtualbox and have parsed the ACPI, FACP, DSDT etc tables to get the PM1a_CNT and SLP_TYPa values. These seem to be correct. However when I try to do an ACPI shutdown with:

xor eax, eax
mov edx, [PM1a_CNT]
mov ax, [SLP_TYPa]
or ax, (1 shl 13)
out dx, ax

Nothing happens. PM1a_CNT is 0x4004 and SLP_TYPa is 0, which seems reasonable compared to other values I have seen elsewhere. I also check PM1b_CNT which is zero so I don't bother with it.

Is there an issue or trick with virtualbox to get it working?

score 2 · Answer 1 · answered Sep 21 '16 at 00:35

2

Everything looks correct except that you're writing a 32-bit value to a 16-bit I/O port. Try replacing the final out dx, eax with out dx, ax.

answered Sep 21 '16 at 00:35

icecreamsword

897
7
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Yeah I initially used ax, didn't work, so I tried eax. Forgot to change it back when pasting the code. Will fix it. – poby Sep 21 '16 at 01:51
So changing it doesn't fix your problem? – icecreamsword Sep 21 '16 at 02:15
No, like I said, I originally used ax and it didn't work – poby Sep 21 '16 at 03:51

how to acpi shutdown in assembly in custom os?

1 Answers1